The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Internal combustion engines have air intake systems which use air filtering devices to prevent ingestion of harmful particles into the engine and combustion chambers. The service life of an element for an air filter varies depending upon operating environment of the engine. For example, a vehicle used in a primarily dusty environment requires more frequent service to and/or replacement of the air filter element than a vehicle used in a clean environment. Delay in servicing an air filter element can result in increased engine pumping losses, which can lead to reduced fuel economy. Vehicle driveability performance can also deteriorate.
A filter element that is unduly plugged can become an airflow restriction, meaning that there is a discernible pressure drop across the air filter. When airflow through the filter element increases, such as at high engine speed and load conditions, the pressure drop increases, which results in the aforementioned increase in pumping losses.
Prior art systems to monitor air filter element plugging have used pressure drop measurements or other indicators to determine when to service and replace the filter element. Some prior art systems have incorporated a barometric pressure sensor upstream of the air filter element which can be used to monitor pressure drop through the air intake system, including a pressure drop across the filter element. Other systems have incorporated control algorithms to determine pressure after the filter and upstream of a throttle valve, in order to determine barometric pressure, which can also be used to monitor pressure drop across the filter element.
Barometric pressure varies with weather conditions and altitude. In a motor vehicle, an accurate determination of barometric pressure is essential for various engine control functions. For instance, precise metering of the amount of air and fuel delivered to the engine is necessary to achieve the desired combustion as well as acceptable vehicle emissions. When the barometric pressure drops, typically ignition timing must be retarded and the air/fuel mixture richened. In addition, the barometric pressure may also be used to control idle bypass airflow, check for limp-in conditions and perform diagnostic functions.
Barometric pressure can be measured in a variety of ways. Currently, in automotive applications, the barometric pressure can be measured using a barometric pressure sensor mountable on any suitable place on the vehicle where it sees true atmospheric pressure. Such a sensor generates an output signal indicative of the atmospheric pressure. The barometric pressure reading is then used for the various engine control functions. However, barometric pressure sensors can be costly and it is always desirable, particularly in automotive applications, to minimize costs.
Methods have been developed for estimating barometric pressure without the use of a separate or dedicated barometric pressure sensor. It is known, for example, that barometric pressure can be estimated when the vehicle's throttle is wide open (i.e., WOT) and, in some cases, when the vehicle's throttle is at some part throttle positions using an existing manifold absolute pressure sensor. However, there is typically a lower throttle position threshold below which barometric pressure cannot be estimated reliably when the engine is firing or rotating.
On a vehicle equipped with a hybrid powertrain, i.e., an internal combustion engine coupled to an electro-mechanical or hydro-mechanical transmission, the engine typically employs an electronic throttle control system, which decouples operator throttle pedal input from throttle valve control. Engine operation on a hybrid powertrain may include prolonged operation at or below the lower throttle position threshold for estimating barometric pressure, and fewer opportunities for WOT events, thereby resulting in unreliable barometric pressure estimates. The result of such operation is barometric pressure values are infrequently updated and thus become ‘stale’ and unreliable for monitoring the air filter element.
Thus, it is desirable to have a reliable method for monitoring an intake air system including the air filter in a hybrid vehicle.